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Патент USA US3031325

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April 24, 1962 I
Filed March 16, 1960
S Sheets-Sheet 1
April 24, 1962
Filed March 16, 1960
3 Sheets-Sheet 2
April 24, 1962
Filed March 16, 1960
3 Sheets-Sheet 3
500- %\
200' /
20 -
Temperature, °F.
F I G. 6
8| R.M. REEVE.
3,®3 1,3 14
Patented Apr. 24, 1952
v 3
Carl E. Handel, George K. Nutter, and Roger M. Reeve,
Berkeley, Caliti, assignors to the United States of
America as represented by the Secretary of Agriculture
Filed Mar. 16, 1960, Ser. No. 15,508
4 Claims. (Cl. 9?--207)
(Granted under Titie 35, US. Code (‘1952), see. 266)
A non-exclusive, irrevocable, royalty-free license in the
less ‘sticky than those cooked by conventional methods.
. As a consequence, subsequent procedures are simpli?ed.
For example, the cooked potatoes can be granulated more
readily. That is,- they can be readily subdivided into‘
?ne particles without cell rupture. Also, potatoes cooked
in accordance with the invention require less time of
conditioning to put them in a granulable state as com
pared with potatoes cooked by present methods.
The cooking technique of the invention results in uni
invention herein described, throughout the world for all 10 form cooking throughout the potato pieces with resulting
, purposes of the United States Government, ‘with the
uniformity of the dehydrated product eventually pro
power to grant sublicenses for such purposes, is hereby
With conventional cooking methods, surface
granted to the Government of’ the United States of
layers tend to be over-cooked while inner portions tend
be under-cooked. Such eli'ects leads to graininess of
This invention relates to and has among its objects the 15 to
portions of the product and stickiness of other por
provision of novel processes for preparing dehydrated
tions when the product is reconstituted.
potatoes. A particular obiect of the invention concerns
The cooking process of the invention yields products
the provision of improvements in the cooking, stage of
may be reconstituted with boiling water to pro
the process whereby to facilitate subsequent steps and to
of a desirable mealy texture, free
obtain products of new and improved properties. Fur 20 from pastinesspotatoes
or graininess.
ther objects and advantages or" the invention will be
Moreover, the products of the invention may be ‘re
evident from the following description taken in con
constituted with water at room temperature. This method
nection with the annexed drawing. Parts and percentages
of reconstitution is of special advantage Where the dried
set forth herein are by weight unless otherwise speci?ed.
product is formed into mashed potatoes for freezing
In the drawing, FIG. 1 is .a schematic ?owsheet illus
trating procedures embodying the principles of the in
vention. FIG. 2 is a view, partly in cross-section, of a
granulator device useful for carrying out various steps
in the process, including conditioning and drying as well
as granulation.
FIG. 3 is a cross-sectional end view
taken on plane 3—3 of FIG. 2. FIG. 4 illustrates the
granulator used in conjunction with a collecter for re
ceiving dried product. vFIG. 5 illustrates another form of
preservation, for example, in putting up frozen,v ready
cooked dinners which merely require heating to make
them ready for the table. In producing these ready
cooked dinners, it is highly desirable to use room-tem
perature water for reconstitution to eliminate need for
cooling prior to freezing.
Another point is that the products of the invention will
absorb more water than productsmade with conventional
cooking procedures. As a result, the products of the in
apparatus for conditioning, granulating, drying, etc.
FIG. 6 is a graph illustrating the temperature and time 35 vention will provide a greater amount of reconstituted
mashed potatoes as compared with an equal weight of
conditions in the cooking stage.
conventional products.
In the preparation of dehydrated potato products, it
is conventional to cook the raw potatoes at an early stage
potatoes under controlled conditions. The conditions of
in the process. For example, cooking is applied in pre
paring all the dried products which are intended to be 40 cooking have been found to be critical and the improved
results of the invention are attained by a correlation of
table-ready on reconstitution of the dried product. No
time and temperature. The inter-dependence of these
table among such products are dried potato tlakes and
dried potato granules. The latter terms are conven- . variables is best explained by reference to FIG. ,6 in the
annexed drawing. In ‘this ?gure, the minimum and maxi
tionally employed as designating dehydrated, pre-cooked
mum cooking times corresponding to diiiere'nt cooking
potatoes in ?ake and granular form, respectively. The
cooking procedure presently employed in preparation of
the various products is essentially the same as ordinary
home-cooking methods. That is, the raw potatoes in
the form of slabs or thick slices (about 3%" thick) are
boiled in water until tender. Sometimes steam, instead,
of boiling water, is applied to the potato pieces. In either
case, the cooking is continued for about 20 to 30 min
The cooked potatoes while hot are then mashed
and eventually dried in particulate form. Various spe
temperatures are plotted with the temperature on a linear
scale and the time on a logarithmic scale. Curve AB
represents the minimum cooking conditions while curve
CD represents the maximum cooking conditions. Thus,
for example, if a cooking temperature of 180° F. is
chosen, the potatoes are cooked from 75 to 420 minutes.
ther conditions which may be used are, by Way of ex
ample: At 190° F., 30' to 180 minutes; at 200° F., 12 to
45 minutes; at 212° F., 5 to 10 minutes. By operating
cialized steps are employed depending on the, type of 55 Within the area ABDC, many signi?cant advantages are
gained. Most important is that the potatoes are properly
product to be produced. For example, in preparing dried
potato granules by the widely-used “add-bacldlnethod,
the mashed potatoes are mixed with su?lcient dried po
tatoes from a previous batch to give a moisture content
cooked yet the ?nal dried products are not sticky on re
Moreover, operations subsequent to the
cooking. step are simpli?ed and'take less time. For ex
of about 32 to 35% for the composite material. This 60 ample, in the manufacture of granules, conditioning under
identical conditions will require one-half or less time
material is then ‘cooled and conditioned by holding it at
about 60 to 80° F. for an ‘hour or more. ‘ The conditioned
than potatoes cooked by conventional methods. Also,
the potato material can be readily subdivided without cell
composite material is then dehydrated in a pneumatic
damage, thus to produce products free from stickiness on
drier to produce the dried granules.
Heretoiore it has not been recognized that the method 65 reconstitution. Other advantages have been mentioned
of cooking has a profound effect on the properties of the
above or are discussed ‘below in connection with operat
ing outside of the preferred range.
dehydrated product nor on the various procedural steps '
leading to the product. In accordance with the inven
Our researches have shown that where the cooking is
tion, the cooking is conducted under special conditions—
carried out under conditions falling below curve AB, in
described hereinafter—whereby many signi?cant advan 70 ferior results are attained. Under such condtions, there
tages are obtained, including the following:
Potatoes cooked in accordance-with the invention are
are many uncooked particles and when the potato ma
terial is treated in subsequent steps, so much mechanical
force must be applied to subdivide these particles that
while at the same time removing moisture from it. That
extensive cell rupture occurs. As a result, the ?nal dried
is, the intensity of the mechanical forces are so con
trolled as to achieve effective separation of one cell from
another rather than rupture of individual cells. As a
product on reconstitution forms a mass of undesirable
pasty texture. Also, if the cooking is carried out under
net result, the potato material is formed into ?ne parti
conditions falling above curve CD inferior results are ob
cles so that the end product will reconstitute rapidly and
tained, these involving either (a) discoloration and de
directly forming mashed potatoes free from lumpy or
velopment of off-?avors, or (b) development of sticki
gritty particles. Further, because cell rupture is kept at
ness these respective defects depending on the tempera
a minimum, the reconstituted product is free from pasti
ture used. Thus, at the higher temperature ranges, about
ZOO-212° F., cooking above curve CD leads to stickiness 10 ness. In preparing granules without add-back, this im
proved method of subdivision is preferably applied after
so that long conditioning times are required and subdivi
the potatoes have been subjected to a series of steps
sion without cell rupture is ditiicult to accomplish. At
usually including cooking, mashing, and partial drying,
lower temperature ranges, about 175—195° F., cooking
above curve CD leads to discoloration (browning) and
development of unnatural, undesirable ?avors.
Generally it is preferred to carry out the cooking at a
temperature of about 190° F. for the reason that at this
temperature there is greater leeway than at higher tem
peratures between minimum and maximum cooking
Thereby the process can be more accurately con
trolled and variations due to differences in composition
of different batches of potatoes, localized or temporary
temperature changes in the cooking medium, and the
like, are canceled or at least minimized.
Also, at the
The subdivision step may be performed as a separate step
or as part of other steps in the sequence of operations.
Thus, for example, the potatoes may be cooked, mashed,
partially dried, conditioned by known methods, sub
divided in accordance with the invention, and ?nally
dried. More preferably, the conditioning step is carried
out while also applying the subdivision treatment. In
this way the time of conditioning is substantially reduced
and the potato material is more readily reduced to ?ne,
non-coherent particles. Another preferred plan is to ap
ply the subdivision treatment during the ?nal drying
lower temperature range, 175-190” F., the thickness of
the potato slices which are to be cooked is immaterial,
stage as well as in an earlier stage.
center of the piece or slice is undercooked while the sur
cance of the subdivision.
This has the bene
?t that the ?nal product is in especially ?ne particle size
and exhibits a high density-very important in reducing
and can be as much as one or two inches, or moderate
packaging costs of the final product. It is evident from
sized potatoes can even be cooked whole, Without ap
the above that Where the subdivision step is applied in
preciable non-uniformity of cooking through the ma
terial. At higher cooking temperature it becomes more 30 conjunction with another treatment, for example, con
ditioning or drying, it loses its identity as a separate, in
important that slice thickness or piece size be small
dividual step. This, of course, does not belie the signifi
enough to avoid non-uniformity of cooking whereby the
face is overcooked, with resultant loss of the bene?cial
effects of the new cooking procedure. Thus at the high
est cooking temperatures, about 205 to 212° F., it is
preferred to use slices up to and including about one
half inch, or other pieces with similar ratio of surface
area to volume, for example, dice up to and including
once inch on a side.
The cooking, carried out under the conditions of time
and temperature as explained above, is generally eifected
by immersing the potato slices in a bath of water at the
selected temperatures.
Another plan is to subject the
potato slices to a current of steam or other hot gases.
For cooking at temperatures below 212° F., mixtures of
steam and air proportioned to provide the selected tem
perature, are useful.
It is to be noted that in the method of the present in
vention, the raw potatoes are given a single cook at pre
scribed conditions of time and temperature. This proce
dure is in contrast with methods which have been previ
ously advocated wherein the potatoes are given a pre
cook at relatively low temperatures followed by a cook
at boiling temperatures.
The potatoes, cooked in accordance with the invention,
may be subsequently treated by any of various processes
which lead to the production of dried potatoes in particu
late form. Regardless of the type of product eventually
produced, the advantages outlined above will be realized.
As examples, the cooked potatoes are mashed and then
treated by known procedures to produce dried ?akes or
For a complete understanding of how the principles of
the invention are applied in practice, the following de
tailed description is provided:
Referring to FIG. 1 in the annexed drawing, in stage
1 the raw potatoes are subjected to the usual preliminary
steps of washing, peeling, trimming, and slicing. The
40 tubers are cut into slices which may range about from
one-eighth to one inch in thickness. To preserve ?avor
and color, it is preferred to dip the slices in a sulphite
solution prior to further treatment. Usually an aqueous
solution containing about from 0.5 to 1.25% of sodium
r sulphite or bisulphite is used and the slices dipped there
in for a few minutes. For example, slices a quarter inch
thick are dipped one minute in a 0.5% sulphite solution
while slices three-fourths inch thick are dipped ?ve
minutes in a 1.25% sulphite solution. Usually the con
ditions of dipping are adjusted so that the slices contain
about from 200 to 500 parts per million (p.p.m.) of S02
on a dry basis. Sulphiting may be applied at this stage
as just described, but as an alternative it may be applied
at a later stage, for example, after cooking and mashing.
Another alternative is to apply part of the sulphite as
described above and a further amount after cooking and
mashing. Another alternative is to apply all or part of
the sulphite by adding sulphur dioxide to the air or other
gaseous medium applied to the potatoes during such steps
as conditioning, granulating, drying, etc. Also, all or part
of the sulphite may be applied in the soaking step de
scribed below.
Techniques for converting mashed potatoes
An advantageous procedure which may be applied to
into such products are well known in the art and any of
the raw potato slices is to soak them in water to increase
their moisture content. This has the desirable effect that
the procedures may be employed. Techniques for pro
ducing granules are disclosed, for example, by Neel et
a1., Food Technology, vol. VIII, pp. 230-234, 1954, and
processes of producing ?akes by Willard et al., U.S.
Patent 2,780,552.
the dehydrated products produced therefrom display an
abiilty to absorb more water on reconstitution than
otherwise would be the case. The procedure employed
simply involves soaking the raw slices in water until their
weight increases about 10% by absorption of Water. De
A preferred technique of converting the potatoes,
pending on such factors as piece size, variety of potato,
cooked in accordance with the invention, into dried
etc., the soaking to attain this effect may require any
granules without necessity for “add-back” is disclosed be
where from one to four hours. The soaking step if
low. A principal feature in this procedure is that sub
employed is a useful point at which to impregnate the
division is accomplished by subjecting the potato ma
terial to repeated mild compression and mild shear forces 75 potato tissue with sulphite. Hence, the water may con
tain a small proportion, say 0.02 to 0.1% of sodium
sulphite or bisulphite. This sulphiting procedure may be
used instead of, or in conjunction with, sulphiting at
other stages in the process.
In stage 2, the potato slices are cooked under controlled
conditions of time and temperature as described above.
In stage 3, the cooked potatoes—while hot-are mashed
in conventional manner. This operation may be carried
out by pressing the cooked potatoes between warm rolls,
by pressing them through a screen, or by other conven
simultaneously contacting it with a stream of air. Under
‘these conditions, and especially when the potatoes are
cooked in the special way described above, the condition
ing above freezing temperatures is completed in a maxi
mum of three hours and in many cases in one to two
hours. More frequent mixing or ?u?ing is required When
the mash is being cooled than at other times during the
conditioning, because the hardening of the mass is ac
celerated by the evaporation of moisture from the product
during cooling. The mixing or ?uf?ng is a form of the
mild compressive-mild shear action. It is important that
tional potato-mashing techniques. During or after mash
ing, various additives may be incorporated into the mash.
the compressive portion of the forces be especially mild
Thus, to preserve color and ?avor, a minor proportion
in the early stages of conditioning. Otherwise, the ma~
of sodium sulphite or bisulphite may be added, Gener
terial, which is somewhat cohesive in these early stages,
ally, enough sulphite is added to provide about 200 to 15 will
be agglomerated by the action, rather than separated,
‘500 ppm. of S02 on a dry basis, including that incor
and longer time will be required for the material to be
porated in the previous sulphite dipping step or other sul
come friable.
phiting operation, where such are used. Minor propor
In stage 6, ‘the conditioned material is granulated and
tions of fat-stabilizing antioxidants such as nordihydro
dried through the critical moisture range. The granula
guairetic acid, butylated hydroxy anisole, butylated hy
droxy toluene, etc., may be added to prevent rancidi?ca
tion of the natural fat in the product on storage. To in
crease ability of the product to absorb moisture and to
reduce stickiness, edible dispersing agents such as the
20 tion and drying are carried out either simultaneously or
in closely successive operations repeated a number of
times. (Where conditioning is carried out at subfreezing
temperature, the mash is thawed before granulating.) In
this granulating step the aim is to subdivide the mash into
monoglyceryl esters of long-chain fatty acidsmay be in 25 particles
containing not more than about ten individual
corporated in the mash. Other substances which may be
cells, preferably unicellular particles, and it must be done
added are such food ingredients as salt, whole milk solids,
by separating one cell from one another rather than by
non-fat milk solids, etc.
rupturing individual cells. Were the latter to be done the
In stage 4, the mashed potatoes are partially dehydrated.
product would yield a pasty, unpalatable mass on recon
This may be conveniently done with a double-drum drier.
stitution, 'Ihe granulation can be successfully accom
The mashed potatoes are fed into the nip between rotating,
plished by applying to the mass repeated mild compression
heated drums and the partially dried potato material is
and mild shear forces. Preferred methods by which this
removed by scraper blades. The drier drums are gener
end can be attained are explained below in connection
ally heated to a temperature in the range about from 150
with FIGS. 2, 3, and 5.‘ Any coarse potato material pre
to 300° F. The temperature of the drums, the speed of 35 sent after granulation may be recycled back to the condi
rotation, and the thickness of the ?lm of potato material
tioning step (stage 5).
are so correlated that the partially dried potato mash has
In stage 7, the granulated potato material is further de
a moisture content about from 50 to 75%, preferably
hydrated to produce the dried granules. This ?nal de
about 60%. Although partial drying on heated drums is
hydration may be carried out in any manner as is con
a preferred technique, it is notessential to use it. Thus 40 ventional in the art. As an example, the potato material
other conventional dehydration procedures such as expos
may be dehydrated by procedures incorporating the prin
ing thin layers or extruded portions of the mash to a cur
ciple of ?uidization. To this end, the potato material is
rent of hot air, vacuum dehydration techniques, and so
placed in a vessel provided with means for jetting minute
forth, can be employed.
of hot air up through the bed of material tending
Following partial drying, the potato material in stage 5 45 to keep it in a ?uidized state while being dried. Apparatus
is subjected to cooling and conditioning to eliminate its
of this type and method of employing it to dehydrate
doughy texture and make it friable. In this stage the
moist potato particles are disclosed by Neel et al. (Food
temperature of the mash is reduced to temperatures rang
Technology, 1954, vol. VIII, pp. 230-234.) To further
ing from about 100° F. down to subfreezing tem eratures.
promote ?uidization of the product in the early part of
The conditioning may be effected in various ways. For
this drying operation, this ?uidized-bed drier can be sub—
example, the potato material may be held without mixing
jected to continuous vibration or shaking, or a mechanical
in closed containers in the presence of adventitious air
agitator can be employed. In the alternative, the granu
or in the absence of air, that is, under vacuum or in an
lated potato material may be dehydrated in pneumatic~
atmosphere of an inert gas such as nitrogen. Where the
type drielis, for instance, a device of the type disclosed
conditioning is at temperatures above freezing, the mash 55 by
()lsonlet al. in Food Technology, vol. VII, pp. 177
may be subjected to occasional or periodic ?u?ing or mix
181 (1953).’ This device consists essentially of a long,
ing during conditioning to minimize formation of aggre
vertically positioned duct. Hot air at about 2l2-392°
gated masses vthat would subsequently be di?icult to sep
F. is forced upwardly at high velocity (i.e., about 1000
arate without rupture of cells. Thus, for instance, ‘the
ft./min.) through the duct and the friable granulated po
potato mash may be‘ carried on an elongated conveyor 60 tato material is fed into this air stream. As the current
belt while it is subjected to the action of rotating paddles
of air carries the material upward it is dehydrated. At
or similar devices which exert a gentle mixing or ?u?ing
the top of the duct is a conically diverging diffuser so
action to effect separation of the mass Without rupture
that as the current rises into the diffuser its velocity is
of individual cells. During the conditioning, the mash
gradually diminished. A deflector is positioned above the
may be contacted with a current of air or an inert gas 65 diffuser whereby the now slowly moving current is de
such as nitrogen to cool the product to temperatures from
?ected downward causing the dried potato granules to
about 100° F. down to about 30° P. if conditioning is
drop out of the air stream so that they can easily be sep
above freezing, or to freeze the product if conditioning
arated from‘the moist exhaust air. In a preferred method,
is brought ‘about by freezing. A minor proportion of
sulphur dioxide may be added to 'the gas stream, particu
larly in the event that in previous steps the usual amount
of sul?te is not added to the mash. In the preferred
the ?nal dehydration is accomplished while the potato
material is subjected to repeated mild compression and
mild shear forces, as described below in connection with
FIG. 4. ‘In any event, after ?nal drying the product has
modi?cation the conditioning is carried out by applying
a moisture content of about 5 to 8%, preferably ‘about
to the mash occasional or periodicimixing or ?uf?ng while 75 6%.
Reference is now made to FIGS. 2 and 3 which illus
trate one modi?cation of apparatus for effecting the gran
ulation and drying through the critical moisture zone.
The apparatus, generally designated at 20, comprises a
trough or U-shaped chamber 22 provided with a remov
able lid 23 and a longitudinal shaft 24. Suitable equip
ment, not illustrated, is provided to rotate shaft 24 in the
direction shown at a low speed—-about 1 to 5 r.p.m.
Attached to shaft 24 are a series of arms 25, each bearing
a paddle 26. Dimensions are so chosen that the tips of
paddles 26 have a clearance on the order of one-fourth
to one-half inch from the cylindrical base of trough 22.
Also positioned on shaft 24 are arms 27 which carry a
the potato material is so horny that it cannot be sub
divided without cell rupture. However, where the gran
ulation is conducted while repeatedly applying the mild
compression and mild shear forces and simultaneously
contacting the mash with a draft of drying gas, this treat
ment being continued while the moisture content of the
mash passes through the range from about 50% moisture
down to about 35% moisture, the potato material is
effectively granulated without cell rupture and the gran
ulated product displays a minimum tendency to cohere
in subsequent operations. In operating under this sys
tern, it is evident that there is at least a partial merging
of stages 6 and 7 because in both of these stages there
is granulation as well as drying.
The apparatus illustrated in FIGS. 2 and 3 can be em
22. Blade 28 is made of ?exible material such as silicone 15
ployed for drying the granulated potato material. In
rubber (Silastic), neoprene, Te?on or other elastomer
deed, this is a preferred method as it permits reducing
and is so positioned that its edge actually wipes against
the moisture content through the critical zone mentioned
the cylindrical base of trough ‘22. This base may be pro
blade 28 which extends essentially the length of trough
above while simultaneously subjecting it to granulation
vided with small protuberances, as by welding wires lon
gitudinally along it, to increase the shearing effect to the 20 with mild compression and mild shear forces. To this
end the granulator 20 is connected to a product-collection
desired level. An inlet conduit 29 is provided for intro
system as shown in FIG. 4. Referring to this ?gure, the
duction of gaseous media, for example, air for drying.
exit conduit 3t) is connected to collector 21. In opera
In using the illustrated device to granulate the potato
tion, the dried product is carried by the current of air
material, conditioned potato mash-produced as above
described-is introduced into trough 22. Shaft 24 is then 25 out of trough 22 into collector 21, the product dropping
through discharge port 31 and excess drying air being
caused to rotate and drying air is introduced through
released through vent 32. In drying in this way, the
inlet conduit 29. The resulting action of paddles 26 and
‘amount and temperature of the air introduced into the
blade 28 effect the granulation of the potato material.
Thus, paddles 26 cause a repeated mixing of the material 30 system via conduit 29 are increased above the levels used
in the preceding stage. Thus, for example, the air tem
and a ‘disintegration of the larger aggregates of cells.
perature used is about from 150 to 250° F. The velocity
Blade 28 being actually in contact with the cylindrical
base of trough 22 effects a further size reduction of the
of the air is increased so that the current is strong enough
very readily separated from one another. This is at the
rial may ‘be introduced into trough 22 and shaft 24
started to rotate, this being continued throughout the
process. At ?rst, air at about room temperature is intro
duced into the system through conduit 29. Then as the
to carry out from trough 22 the ?ne dry particles. Dur
particles. The reduction in particle size effected by the
device is essentially limited to separation of individual 35 ing the drying cycle, shaft 24 is rotated, as during the
granulation, to maintain the potato material in a loose
cells one from another as contrasted with rupture of in
bulky state and subdivide any larger particles found
dividual cells. Important in this regard is the fact that
by re-aggregation of ?ner ones. During operation, the
paddles 26 and blade 28 exert what may best be termed
particles discharged from pipe 31 are examined and the
as mild compression and mild shear forces. Thus the
mechanical forces exerted by these elements are of suffi 4-0 velocity of the air stream adjusted so that essentially only
the properly-dried, ?ne particles are carried by the air
cient intensity to separate agglomerated cells but insu?i
stream into the collector and the aggregated particles
cient to rupture individual cells. The action is continued
remain in chamber 22 for further drying and subdividing.
until the potato material forms a well-granulated mass
It is further evident that granulation and drying need
of unicellular particles and small aggregates of unicellu
not necessarily be carried out as separate and distinct
lar particles that have only a very slight tendency to
steps. Thus, for example, the conditioned potato mate
agglomerate together. Any agglomerates formed are
lower end of the critical moisture region where the
potato material contains about 32 to 45% water, the pre
cise moisture value depending somewhat on the previous
history of the material.
During the granulation, the
potato material is contacted with a current of air, for
example, at a temperature about from 75 to 200° F., to
cause the desired reduction in moisture content during
Ordinarily, the product remains at room
temperature (about 75° F.) during the granulation. The
warm air introduced does not appreciably raise the tem
operation continues the air temperature is gradually in
creased up to suitable temperatures for drying. Like
wise, during the later stage of the process, the velocity
of the air stream is likewise increased to entrain the
dried ?ne particles and carry them out of the trough.
Moreover, the trough granulator may be used for all
three stages—conditioning, granulation, and drying.
perature of the potato material because of the cooling
Thus, for example, the partially-dried hot mash is intro
potato material, as regards granulation, and its moisture
cooling may be applied as by contacting the mash with
duced into trough 22 and shaft 24 rotated either contin
effect as water is evaporated therefrom.
Moreover, our researches have shown that there is an 60 uously or at intervals until the mash loses its doughy
texture and becomes more friable. During conditioning,
important relationship between the properties of the
Knowledge of this relationship permits us to
air at room temperature or below.
After the potato
obtain signi?cant advantages in the production of potato
material begins to lose its doughy texture, the shaft is
critical moisture range. Thus, our researches have indi
tually, the velocity of the air stream is increased to en
train the ?ne dry particles and carry them out of the
trough into the collector system.
In FIG. 5 is illustrated an alternative form of apparatus
granules. It has been found that the granulation is most 65 rotated continuously, this being continued throughout
the process, while the air temperature is gradually in
effectively accomplished while the moisture content of
creased up to suitable temperatures for drying. Thereby
the potato material is reduced from about 50% down to
the product is subjected to granulation and drying. Even
about 35%, this range being herein designated as the
cated that if the granulation is applied only at higher
moisture levels (that is, above about 50%) the product
retains so much cohesiveness that the particles will re
which may advantageously be utilized in the conditioning,
aggregate when subjected to subsequent operations. On
granulating and drying steps. This apparatus includes a
the other hand, if the granulation is not effected until the
moisture content of the mash is reduced to below 35%, 75 rectangular frame 35, supporting a screen 36. This screen
is of v?ne mesh construction (80- to lSO-mesh, for in~
stance) to allow air 1to ?ow-through but to prevent the
potato material from passing through it. Frame 35 is
connected to vibrator 37, of conventional construction,
to vibrate the device.
'Journaled on frame 35 are a series
In the examples, products were tested for blue value
index by the method of Mullins et al. (Food Technology,
vol. 9, p. 393) on a basis of 21/: grams of dry solids. This
determination furnishes a measure of release of free starch
from'the cells and a higher value denotes more free starch.
of shafts 38 rotated in the direction shown by suitable
equipment at moderate speed (about 50 to 150 r.p.m.).»
In another test, moisture absorption of the products was
whereas the soft, ?exible, elastic blades 28 actually con
mashed potatoes are formed from a standard amount of
measured by a modi?cation ‘of the method of Potter
Secured to shafts 38 are arms 25 and 27, hearing paddles
\(Iour. Ag. and Food Chem., vol. 2, p. 516; 1954). This
26 and blades 28, as described in the modi?cation of FIGS.
test determines the volume of reconstituted mashed po
2 and 3. As in that modi?cation, paddles 26 clear screen 10 tatoes formed per unit weight of dried granules. In this
36 by a distance of about one-eighth to one-fourth inch
case a higher value indicates a superior product as more
tact ‘the screen. In using the device the potato material
dry material.
is placed on the screen 36 at the upper (right-hand) end
Example I
and shafts 38 are rotated while ‘the frame is vibrated. In 15
potatoes were washed, peeled,
small-scale construction the material arriving at the lower
trimmed, and cut in three-fourths inch thick slices.
end of the screen may be collected and replaced at the
The‘slices were dipped five minutes in a 1.25% aqueous
higher end for continued action. On a larger scale the
solution of sodium bisulphite. The slices were then
dimensions and the number of shafts and associated mech
cooked 60 minutes in a mixture of air and steam having
anisms are selected to properly treat the material in a
a temperature of 190° F.
single pass. The device, as that‘of FIGS. 2 and 3, may
The cooked potatoes were mashed by pressing through
be employed in any of the stages of conditioning, granu
a one-half inch mesh screen, then blended in a planetary
lating, dr-ying, or any combination of them. Air for de
type mixer for one minute with 10% of their Weight of
creasing the moisture content of the potato material dur
ing treatment is forced upwardly through duct 39‘, con 25 water containing 0.6 gram of sodium bisulphite per ten
pounds of potatoes.
nected to frame 35 via ?exible coupling 40. Where the
The potato mash was then partially dried on a single
system is used for producing a dry product, a hood and
drum drier-drum temperature 250° F., speed of drum
collector of conventional design may be positioned above
2.5 r.p.m.‘ The partially-dried mash had a moisture con
frame 35 for collecting the dried product.
As has been noted brie?y above, the present invention 30 tent of 56.5%.
The partially-dried mash was then conditioned. To
may advantageously be applied in the manufacture of po
this end, it was placed in a trough granulator as depicted
tato granules by the add-back process whereby to obtain
in FIGS. 2 and 3. The shaft was rotated (2 r.p.m.) con
signi?cant advantages including (1) elimination or at
tinuously during addition of the mash (30 minutes), then
least marked reduction in time of conditioning, (2) reduc
for the next hour the shaft was rotated ?ve minutes out
tion in amount of “seed” which needs to be recycled and
(3) reduction in stickiness of the ?nal product on re
of each 15-minute period. During this operation the tem
constitution. Thus advantages result from the fact that
with the new cooking procedure there is (1) substantially
improved granulability of partially dried potatoes, and
(2) much improvement in texture of the ?nal product. 40
perature of the mash decreased from about 125° F. to
about 65° F. The mash was then friable and ready for
the beginningof granulation. It was near the upper limit
of the critical moisture region referred to above.
To granulate the conditioned mash, it was left in the
In applying the invention to the add-back process, potatoes
trough granulator and the shaft was operated continuously
are subjected to the preliminary steps (stage 1) and to the
(2 r.p.m.) for one hour while air at room temperature
new cooking procedure (stage 2) as described above.
was blown through the device. Moisture content of the
The cooked potatoes are then mashed and mixed with
su?lcient “seed” granules‘ (that is, dried granules from a 45 material was reduced to 50.5%. The material was near
the middle of its critical moisture region. It was now
previous batch) to form a composite having a moisture
granulated well enough that the rate of drying could be
content of about 32 to 35%. This composite material is
increased without resulting in an excessive proportion of
then cooled to about room temperature, preferably while
coarse dried product.
applying‘repeated'mild compression and mild shear forces
The potato material-—still in the trough granulator and
as described above, using the granulator device of FIGS. 50
with the collector attached as in FIG. 4——was subjected
2 and 3 or that of FIG. 5. The material can then be
to a current of air at 200°
while the speed of the shaft
dried directly-—no conditioning step is required as in
was increased to 5 r.p.m. yIn about 30 minutes, 94% of
previous practice. Thus in conventional practice the
the dried granules were received in the collector. This
composite (freshly mashed potatoes plus seed granules)
must be conditioned at room temperature for at least an 55 product containing 20% moisture was then ?nish-dried in
a ?uidized bed drier to produce granules of 6% moisture
hour. In an alternative method, the present invention
content. The product had a blue value index of 17, in
maybe used in the manufacture of potato granules by the
dicative of very slight cell damage. Bulk density of the
add-back process to obtain a product of very ?ne texture
product was 0.92 gram/cc; moisture absorption was 5.7
(unusually low blue value), again without conditioning of
the material before drying. (Elimination of the condi 60 cc. of reconstituted mash per gram of product. A portion
otthe product on reconstitution‘with boiling water formed
tioning period .is important as there is .then much less op
mashed potatoes of a desirable mealy texture free from
portunity for 'quality changes, by oxidation or other de
both pastiness and graininess.
teriorative reactions.) [In applying this process the po
tatoes are treated as above described-preliminary steps
(stage 1), special cooking (stage'2), mashing (stage 3‘),
and partial-drying (stage 4), then mixed with su?icient
Example II
A quantity of Idaho Russet Burbank potatoes was
washed-peeled, trimmed,>sliced, and given a 5-minute dip
“seed” granules to give a moisture content of 30 to 40%
in 1.25 % aqueous sodium bisulphite solution. The ma
for composite material. The composite material is mixed
terial was then divided into several lots which were
and cooled to room temperature, preferably while apply
ing repeated mild compression and mild shear forces as 70 cooked under ditferent time and temperature conditions
set forth below. For comparison, several lots were
described above, using the granulator device of FIGS. 2
cooked under conditions outside ‘the scope of the inven
and 3 or that of ‘FIG. 5. The fl'fl'?lel'ldl'iS them directly
tion; these included lots A1, A4, A5, and Cl.
dried-no conditioning period is ‘needed.
Following cooking, each lot was converted into granules
‘The invention is further demonstrated ‘by vthe following
by the ‘same method. This method involved these steps:
illustrative examples.
The cooked potatoes were mashed by pressing through
The slices were dipped ?ve minutes in a 1.25 %
aqueous solution of sodium bisulphite. The slices were
then cooked for 90 minutes in a mixture of steam and
air having a temperature of 185° F.
The cooked slices were mashed and mixed with 10% of
their weight of water containing 0.6 g. of sodium bisul
a one-half inch mesh screen, then blended in a planetary
type mixer for one minute with 10% of their weight of
water containing 0.6 gram of sodium bisulphite solution
per ten pounds of potatoes.
The potato mash was then partially dried on a single
drum drier—drum temperature 250° F., speed of drum
phite per ten pounds potatoes and with seed granules
using six pounds seed to three pounds cooked potatoes.
(In the ?rst run, the seed was commercial potato granules;
3.5 r.p.m. The partially-dried mash had a moisture con
tent of about 55%.
The partially-dried mash was then conditioned. To
this end, it was placed in a trough granulator as depicted 10 in subsequent runs, the seed was granules from the next
previous run.) The mixing was done in a planetary-type
in FIGS. 2 and 3. The shaft was rotated (2 r.p.m.) con
food mixer and in ten minutes the temperature of the
tinuously during addition of the mash (30 minutes) then
mix was about 110° F. Air was blown into the mixer
the shaft was rotated ?ve minutes out of each 20-minute
for ?ve minutes longer, at which time the mix was cooled
period. In about 90 minutes the temperature of the
mash decreased from about 125° F. to about 65° F. The 15 to about 75—80° F. Mixing was then discontinued.
The cooled composite was then dried in a pneumatic
conditioning was continued until the potato material
(air-lift) drier using a current of air at 260° F.
lost its doughy texture and became friable. The time re
The dried material was screened through an 8-mesh
quired for this result varied with the diiferent lots as
screen, the coarse material retained on the screen being
indicated in the table below.
To granulate the conditioned mash, it was left in the 20 weighed and discarded as “scalping loss.” The ?ne ma
terial was then put through a 60-mesh screen, the ma
terial on this screen being reserved as seed for the next
trough granulator and the shaft was operated continu
ously for one hour while air at room temperature was
blown through the device. Moisture content of the ma
terial was reduced to about 50%.
cycle, the material passing through the screen being the
granule product.
The process as described above was repeated some 15
The potato material-still in the trough granulator and 25
times, each representing a cycle. It may be noted that
it requires about ten cycles to produce representative re
sults, that is, elimination of. the effect of the seed originally
with the collector attached as in FIG. 4-was subjected
to a current of air at 200° F. while the speed of the shaft
was increased to 5 r.p.m. The product received ‘in the
collector, containing about 20% moisture, was ?nish-dried
For control purposes, the same procedure was applied
in a ?uidized bed drier to produce granules of about 6% 30
except that the cooking conditions were conventional.
moisture content.
Thus the potato slices, in this case three-fourths inch
The conditions used and the results obtained are tabu
were cooked in steam (212° F.) for 25 minutes.
lated below:
Size of raw
potatoes, Inches
1% x )4 x %____ 212 (steam) __________ ._
A—2__-_ ,1/2 x V2 x 96 _______ __d
A—3__-_ % x )1; x 12 _______ __do__-__
A-4___- % x % x )5 _______ __do-____
Texture on
Texture on
Cooking tioning
value reconstitution reconstitution
index of with water with water
Min. required, granules at 170° F.
at 212° F.
Cooking temp, ‘’ F.
Good ______ __
Excellent.__. Excellent.
% x % x % _______ __do _______________ __
B .... _.
% (slices)___-_ .200 (steam and air).
2. 5
C-l. ___ % (slices)_C—2____ __.__do___
190 (steam and air)
The results obtained are tabulated below:
Example III
Raw potatoes were cut into free-fourths inch slices and
cooked in a steam-air mixture at 190° F. for various times 50
as described below. Each batch of cooked potatoes was
then separately dried using the following technique. The
With New Cooking With Regular Cook
Method 185° F.,
90 Min.
212° F., 25 Min.
Cycle Number
cooked potatoes were mashed, frozen and while frozen
Value of
Value of
Product Percent Product Percent
extruded through rolls spaced apart 0.01 inch to produce
platelets having essentially monocellular thickness. This 55
product was put on trays and dried in a current of air
at 120° F.
Seed (Commercial granules)"
The various dried products were then subjected to
certain tests. In one test, the products were reconstituted
with boiling water, 90 cc. per 20 g. product, and the re
sulting mashed potatoes were rated for texture, color
and ?avor by a panel of skilled food tasters.
________ __
________ __
.................. __
__________________ _
The results are tabulated below:
The steady improvement in blue value and scalpmg
Cooking Time,
Properties of Reconstituted Product
65 loss in run A (with the new cooking method) as con
trasted with the steady deterioration of quality in run
B (regular cooking) demonstrates the improvement ob
tained with the new cooking method.
Contained uncooked lumps; typical ?avor and color.
No uncooked lumps; typical ?avor and color.
No uncooked lumps; brownish discoloration and
Example IV
Example V
Idaho Russet Burbank potatoes were washed, peeled,
trimmed and cut into three-fourth inch slices.
The slices were dipped ?ve minutes in a 1.25% so
dium bisulphite solution. The slices were then cooked
Idaho Russet Burbank potatoes were washed, peeled
75 for 60 minutes in water at 190° F.
and cut into one-half inch slices.
The cooked slices were mashed and blended with 10%
of their weight of water containing 0.6 g. of sodium bi
sulphite per ten pounds of potatoes. The mash was par
tially dehydrated on a double-drum drier~drum tem
perature 200° F., speed of drums 1 r.p.-m., clearance be
tween drurns 0.015". The partially dried mash had a
and subjecting them to dehydrating conditions to produce
dehydrated potatoes.
2. The method of preparing dehydrated potatoes which
comprises subjecting raw potato slices to a single cooking
operation at a temperature of about 190° F. for about 60
minutes, directly mashing the cooked potatoes and sub
jecting them to dehydrating conditions to produce dehy
moisture content of 75%.
The partially dried mash was then mixed with seed
drated potatoes.
3. The method of preparing dehydrated potatoes which
for the ?rst cycle and material from a previous run for 10 comprises subjecting raw potato slices to a single cooking
granules (3# mash, 4# seed) using commercial granules
the next succeeding cycles. The mixing was in a plane
operation ‘at a temperature of about 190° F. for a period
tary-type ‘food mixer for 15 minutes. The material was
of about 60 minutes, directly mashing the hot cooked
then dried on the vibrating screen drier shown in FIG. 5
potatoes, subdividing the mash into particles and dehy
with parts 27, 28 removed. Air at 190° F. was blown up
drating it to produce dehydrated potatoes in particulate
through screen 316. The product was dried to about 1Q.% 15 form.
moisture content.
4. The method of preparing dehydrated potatoes which
The dried ‘granules were then put through Semesh and
com-prises subjecting raw potato slices to a single cooking
60-mesh screens as described in Example IV.
operation at a ‘temperature of about 190° F. for about
The results are tabulated below:
60 minutes, directly mashing the cooked potatoes, suc
20 cessively subjecting the mash ‘to partial drying, condition
ing, granulating, and ?nal drying to produce dehydrated
potatoes in dry granule form.
Blue Value of
Cycle Number
s--. (Commercial
‘‘‘ " granules) _________________________
' ____ __
References Cited in the ?le of this patent
8 _____ __
Willard _______________ __ Feb. 5, 1957
Oording ______________ __ Apr. 2, 1957
Having thus described the invention, what is claimed is:
1'. The method of preparing dehydrated potatoes which 30
comprises subjecting raw potato slices to a single cooking
Talburt and Smith: 1959, “Potato Processing,” pp.
operation at temperature and time conditions within the
area ABDC in FIG. 6, mashing the potatoes while hot
Talburt: “\P‘otato Processing,” 1959, pp. 330-331.
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